Effect of water activity and temperature on mycotoxin production by Alternaria alternata in culture and on wheat grain

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Abstract
Water activity (aw) and temperature affected the production of altenuene (AE), alternariol (AOH) and alternariol monomethyl ether (AME) by A. alternata on wheat extract agar and wheat grain. Greatest production of all 3 mycotoxins occurred at 0.98 aw and 25.degree. C on both substrates. At 0.98 aw and 25.degree. C, a single colony of A. alternata grown on wheat extract agar produced 807 .mu.g AOH, 603 .mu.g AME and 169 .mu.g AE/ml in 30 days. Production of all 3 mycotoxins at 0.95 aw was < 40% of these amounts. Little toxin was produced at 0.90 aw. Changing temperature and aw altered the relative amounts of the different toxins produced on agar. At 15.degree. C and 0.98 aw, maxima of 52 .mu.g AOH and 25 .mu.g AME/ml were produced after 15 and 30 days, respectively; AE continued to increase and reached 57 .mu.g/ml after 40 days. At 15.degree. C and 0.95 aw, production was, respectively, 62, 10 and 5 .mu.g/ml after 40 days. All 3 metabolites were produced at 5.degree. C and 0.98-0.95 aw and at 30.degree. C and 0.98-0.90 aw. On wheat grain at 25.degree. C and 0.98-0.95 aw, more AME was produced than AOH or AE, but at 15.degree. C there was less AME than AOH or AE. Only trace amounts of AE, AOH and AME were found at 15.degree.-25.degree. C and 0.90 aw, but production of AME was inhibited at 30.degree. C and .ltoreq. 0.95 aw.